The position of a mobile device (device), such as, for example, a cellular telephone, may be estimated based on information gathered from various systems. One such system may include the Global Positioning System (GPS), which is one example of a satellite positioning system (SPS). SPS systems such as GPS may include a number of space vehicles (SV) orbiting the earth. Another example of a system that may provide a basis for estimating the position of a mobile device is a cellular communication system including a number of base stations to support communications for a number of mobile devices.
A position estimate, which may also be referred to as a position “fix”, for a mobile device may be obtained, for example, based at least in part on distances or ranges from the mobile device to one or more transmitters, and also based at least in part on the locations of the one or more transmitters. Such transmitters may comprise SVs in the case of an SPS and/or terrestrial base stations in the case of a cellular communication system, for example. Ranges to the transmitters may be based on one or more signals transmitted by the transmitters and received at the mobile device, and/or vice versa. The location of the transmitters may be ascertained, in at least some example implementations, based on the identities of the transmitters, which may be ascertained from one or more signals received from the transmitters.
In certain Code Division Multiple Access (CDMA) digital cellular networks, a position location capability may apply Advanced Forward Link Trilateration (AFLT) techniques. In certain example Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE) networks a position location capability may apply Observed Time Difference Of Arrival (OTDOA) techniques.
LTE OTDOA positioning technology, by way of example, may use Positioning Reference Signals (PRS) to determine (e.g., measure, calculate, estimate, etc.) a Time Difference of Arrival (TOA) for the positioning signals received from neighboring cells to determine an OTDOA. In order to be able to measure the PRS signals from the serving cell and neighbor cells, a mobile device, may send an assistance data request to an OTDOA system server. Such a server may then send certain assistance data, e.g., possible indicating a suite of cells' information (e.g., Base Station Almanac (BSA) and timing information), to the mobile device. In this example, at least a portion of the information provided to the mobile device by way of such example assistance data may help the mobile device to identify which PRS(s) (cells, transceivers, etc.) to attempt to use for TOA measurements. Note, the terms mobile device, user equipment (UE), and mobile station (MS) are used interchangeably herein and unless otherwise specified are intended to cover any type of electronic device that may participate in the example techniques and/or systems provided herein.
In some instances, an OTDOA measurement may comprise a Reference Signal Time Difference (RSTD). An RSTD may, for example, indicate a relative timing difference between two cells (e.g., a reference cell and a neighbor cell), calculated as the smallest time difference between two subframe boundaries received from the two different cells. The PRS signals may be transmitted by their respective cells on the same carrier frequency (herein, referred to intra-frequency). In other instances, the PRS signals may be transmitted on different carrier frequencies (herein, referred to as inter-frequency). Thus, an RSTD measurement may be calculated for both “intra-frequency” PRS signals and “inter-frequency” PRS signals.
When performing inter-frequency measurements, the mobile device may be configured to either (1) create/use measurement gaps to decode the PRS of the neighbor cell on a single receive chain, or (2) use an alternate receive chain (if the mobile device is configured to use the alternate receive chain and the carrier aggregation combo for the serving cell and neighbor cell band is supported). The measurement gap refers to an interruption/window in the existing receive chain to allow the measurement of a particular PRS of the neighbor cell. Typically, the length of the measurement gap is fixed (e.g., 6 ms). However, a fixed length measurement gap may not be optimal for all cases. Furthermore, excessive current may be consumed when waking up the alternate receive chain periodically for the fixed length measurement gap to monitor the PRS of a neighbor cell.